Conventionally, there has been known a robot that performs voice interaction with a user, which is called a voice interactive robot. However, the voice interactive robot may not correctly recognize a voice made by the user in some cases due to noise output from various equipments in actual environment such as in a home or in an office. To improve a voice recognition rate in the environment where the noise is output by home appliances or by the user's action, it is preferable to input the voice by the user into a microphone at an appropriate level.
There has been proposed a method for improving a S/N ratio by calculating the S/N ratio when the user's voice is detected and by moving the robot toward the user when the S/N ratio is lower than a given value. An example of such method is disclosed in JP-A-2006-181651 (counterpart U.S. publication is: U.S. 2006/0143017 A1). However, according to this method, it is not determined how much the robot needs to move closer to the user for receiving the voice satisfying the S/N ratio sufficient for the voice recognition. Further, when the surrounding noise level is changed, it is required to receive another voice from the user to determine whether or not the distance to the user is appropriate.
There has been proposed a method for indicate to the user an actual voice level and a desired voice level comparatively in accordance with the surrounding noise level to allow the user to intuitively know the desired volume of the voice. An example of such method is disclosed in JP-A-2006-227499. However, a large amount of the voice by the user is heard to the user through a brainpan of the user. Therefore, it is difficult for the user to adjust the volume of the voice in accordance with the indication made by the robot. Also, when the surrounding noise level is changed, the user is required to perform the voice again in order to receive the voice in an appropriate level range.
The above described conventional methods employ a method in which the user's voice level is adjusted through multiple voicees made by the user. Hence, those methods require the user to perform the voice again every time the adjustment is required due to the change in environment such as the change in the surrounding noise level.